// Packaging/modules magic dance.
(function (factory) {
  factory(window.L)
}(function (L) {
"use strict";

L.Polyline._flat = L.LineUtil.isFlat || L.Polyline._flat || function (latlngs) {
  // true if it's a flat array of latlngs; false if nested
  return !L.Util.isArray(latlngs[0]) || (typeof latlngs[0][0] !== 'object' && typeof latlngs[0][0] !== 'undefined');
};

/**
* @fileOverview  Geometry utilities for distances and linear referencing.
* @name L.GeometryUtil
*/

L.GeometryUtil = L.extend(L.GeometryUtil || {}, {

  /**
      Shortcut function for planar distance between two {L.LatLng} at current zoom.

      @tutorial distance-length

      @param {L.Map} map  map to be used for this method
      @param {L.LatLng} latlngA geographical point A
      @param {L.LatLng} latlngB geographical point B
      @returns {Number} planar distance
   */
  distance: function (map, latlngA, latlngB) {
      return map.latLngToLayerPoint(latlngA).distanceTo(map.latLngToLayerPoint(latlngB));
  },

  /**
      Shortcut function for planar distance between a {L.LatLng} and a segment (A-B).
      @param {L.Map} map  map to be used for this method
      @param {L.LatLng} latlng - The position to search
      @param {L.LatLng} latlngA geographical point A of the segment
      @param {L.LatLng} latlngB geographical point B of the segment
      @returns {Number} planar distance
  */
  distanceSegment: function (map, latlng, latlngA, latlngB) {
      var p = map.latLngToLayerPoint(latlng),
         p1 = map.latLngToLayerPoint(latlngA),
         p2 = map.latLngToLayerPoint(latlngB);
      return L.LineUtil.pointToSegmentDistance(p, p1, p2);
  },

  /**
      Shortcut function for converting distance to readable distance.
      @param {Number} distance distance to be converted
      @param {String} unit 'metric' or 'imperial'
      @returns {String} in yard or miles
  */
  readableDistance: function (distance, unit) {
      var isMetric = (unit !== 'imperial'),
          distanceStr;
      if (isMetric) {
          // show metres when distance is < 1km, then show km
          if (distance > 1000) {
              distanceStr = (distance  / 1000).toFixed(2) + ' km';
          }
          else {
              distanceStr = Math.ceil(distance) + ' m';
          }
      }
      else {
          distance *= 1.09361;
          if (distance > 1760) {
              distanceStr = (distance / 1760).toFixed(2) + ' miles';
          }
          else {
              distanceStr = Math.ceil(distance) + ' yd';
          }
      }
      return distanceStr;
  },

  /**
      Returns true if the latlng belongs to segment A-B
      @param {L.LatLng} latlng - The position to search
      @param {L.LatLng} latlngA geographical point A of the segment
      @param {L.LatLng} latlngB geographical point B of the segment
      @param {?Number} [tolerance=0.2] tolerance to accept if latlng belongs really
      @returns {boolean}
   */
  belongsSegment: function(latlng, latlngA, latlngB, tolerance) {
      tolerance = tolerance === undefined ? 0.2 : tolerance;
      var hypotenuse = latlngA.distanceTo(latlngB),
          delta = latlngA.distanceTo(latlng) + latlng.distanceTo(latlngB) - hypotenuse;
      return delta/hypotenuse < tolerance;
  },

  /**
   * Returns total length of line
   * @tutorial distance-length
   *
   * @param {L.Polyline|Array<L.Point>|Array<L.LatLng>} coords Set of coordinates
   * @returns {Number} Total length (pixels for Point, meters for LatLng)
   */
  length: function (coords) {
      var accumulated = L.GeometryUtil.accumulatedLengths(coords);
      return accumulated.length > 0 ? accumulated[accumulated.length-1] : 0;
  },

  /**
   * Returns a list of accumulated length along a line.
   * @param {L.Polyline|Array<L.Point>|Array<L.LatLng>} coords Set of coordinates
   * @returns {Array<Number>} Array of accumulated lengths (pixels for Point, meters for LatLng)
   */
  accumulatedLengths: function (coords) {
      if (typeof coords.getLatLngs == 'function') {
          coords = coords.getLatLngs();
      }
      if (coords.length === 0)
          return [];
      var total = 0,
          lengths = [0];
      for (var i = 0, n = coords.length - 1; i< n; i++) {
          total += coords[i].distanceTo(coords[i+1]);
          lengths.push(total);
      }
      return lengths;
  },

  /**
      Returns the closest point of a {L.LatLng} on the segment (A-B)

      @tutorial closest

      @param {L.Map} map  map to be used for this method
      @param {L.LatLng} latlng - The position to search
      @param {L.LatLng} latlngA geographical point A of the segment
      @param {L.LatLng} latlngB geographical point B of the segment
      @returns {L.LatLng} Closest geographical point
  */
  closestOnSegment: function (map, latlng, latlngA, latlngB) {
      var maxzoom = map.getMaxZoom();
      if (maxzoom === Infinity)
          maxzoom = map.getZoom();
      var p = map.project(latlng, maxzoom),
         p1 = map.project(latlngA, maxzoom),
         p2 = map.project(latlngB, maxzoom),
         closest = L.LineUtil.closestPointOnSegment(p, p1, p2);
      return map.unproject(closest, maxzoom);
  },

  /**
      Returns the closest latlng on layer.

      Accept nested arrays

      @tutorial closest

      @param {L.Map} map  map to be used for this method
      @param {Array<L.LatLng>|Array<Array<L.LatLng>>|L.PolyLine|L.Polygon} layer - Layer that contains the result
      @param {L.LatLng} latlng - The position to search
      @param {?boolean} [vertices=false] - Whether to restrict to path vertices.
      @returns {L.LatLng} Closest geographical point or null if layer param is incorrect
  */
  closest: function (map, layer, latlng, vertices) {

      var latlngs,
          mindist = Infinity,
          result = null,
          i, n, distance, subResult;

      if (layer instanceof Array) {
          // if layer is Array<Array<T>>
          if (layer[0] instanceof Array && typeof layer[0][0] !== 'number') {
              // if we have nested arrays, we calc the closest for each array
              // recursive
              for (i = 0; i < layer.length; i++) {
                  subResult = L.GeometryUtil.closest(map, layer[i], latlng, vertices);
                  if (subResult.distance < mindist) {
                      mindist = subResult.distance;
                      result = subResult;
                  }
              }
              return result;
          } else if (layer[0] instanceof L.LatLng
                      || typeof layer[0][0] === 'number'
                      || typeof layer[0].lat === 'number') { // we could have a latlng as [x,y] with x & y numbers or {lat, lng}
              layer = L.polyline(layer);
          } else {
              return result;
          }
      }

      // if we don't have here a Polyline, that means layer is incorrect
      // see https://github.com/makinacorpus/.GeometryUtil/issues/23
      if (! ( layer instanceof L.Polyline ) )
          return result;

      // deep copy of latlngs
      latlngs = JSON.parse(JSON.stringify(layer.getLatLngs().slice(0)));

      // add the last segment for L.Polygon
      if (layer instanceof L.Polygon) {
          // add the last segment for each child that is a nested array
          var addLastSegment = function(latlngs) {
              if (L.Polyline._flat(latlngs)) {
                  latlngs.push(latlngs[0]);
              } else {
                  for (var i = 0; i < latlngs.length; i++) {
                      addLastSegment(latlngs[i]);
                  }
              }
          };
          addLastSegment(latlngs);
      }

      // we have a multi polygon / multi polyline / polygon with holes
      // use recursive to explore and return the good result
      if ( ! L.Polyline._flat(latlngs) ) {
          for (i = 0; i < latlngs.length; i++) {
              // if we are at the lower level, and if we have a L.Polygon, we add the last segment
              subResult = L.GeometryUtil.closest(map, latlngs[i], latlng, vertices);
              if (subResult.distance < mindist) {
                  mindist = subResult.distance;
                  result = subResult;
              }
          }
          return result;

      } else {

          // Lookup vertices
          if (vertices) {
              for(i = 0, n = latlngs.length; i < n; i++) {
                  var ll = latlngs[i];
                  distance = L.GeometryUtil.distance(map, latlng, ll);
                  if (distance < mindist) {
                      mindist = distance;
                      result = ll;
                      result.distance = distance;
                  }
              }
              return result;
          }

          // Keep the closest point of all segments
          for (i = 0, n = latlngs.length; i < n-1; i++) {
              var latlngA = latlngs[i],
                  latlngB = latlngs[i+1];
              distance = L.GeometryUtil.distanceSegment(map, latlng, latlngA, latlngB);
              if (distance <= mindist) {
                  mindist = distance;
                  result = L.GeometryUtil.closestOnSegment(map, latlng, latlngA, latlngB);
                  result.distance = distance;
              }
          }
          return result;
      }

  },

  /**
      Returns the closest layer to latlng among a list of layers.

      @tutorial closest

      @param {L.Map} map  map to be used for this method
      @param {Array<L.ILayer>} layers Set of layers
      @param {L.LatLng} latlng - The position to search
      @returns {object} ``{layer, latlng, distance}`` or ``null`` if list is empty;
  */
  closestLayer: function (map, layers, latlng) {
      var mindist = Infinity,
          result = null,
          ll = null,
          distance = Infinity;

      for (var i = 0, n = layers.length; i < n; i++) {
          var layer = layers[i];
          if (layer instanceof L.LayerGroup) {
              // recursive
              var subResult = L.GeometryUtil.closestLayer(map, layer.getLayers(), latlng);
              if (subResult.distance < mindist) {
                  mindist = subResult.distance;
                  result = subResult;
              }
          } else {
              // Single dimension, snap on points, else snap on closest
              if (typeof layer.getLatLng == 'function') {
                  ll = layer.getLatLng();
                  distance = L.GeometryUtil.distance(map, latlng, ll);
              }
              else {
                  ll = L.GeometryUtil.closest(map, layer, latlng);
                  if (ll) distance = ll.distance;  // Can return null if layer has no points.
              }
              if (distance < mindist) {
                  mindist = distance;
                  result = {layer: layer, latlng: ll, distance: distance};
              }
          }
      }
      return result;
  },

  /**
      Returns the n closest layers to latlng among a list of input layers.

      @param {L.Map} map -  map to be used for this method
      @param {Array<L.ILayer>} layers - Set of layers
      @param {L.LatLng} latlng - The position to search
      @param {?Number} [n=layers.length] - the expected number of output layers.
      @returns {Array<object>} an array of objects ``{layer, latlng, distance}`` or ``null`` if the input is invalid (empty list or negative n)
  */
  nClosestLayers: function (map, layers, latlng, n) {
      n = typeof n === 'number' ? n : layers.length;

      if (n < 1 || layers.length < 1) {
          return null;
      }

      var results = [];
      var distance, ll;

      for (var i = 0, m = layers.length; i < m; i++) {
          var layer = layers[i];
          if (layer instanceof L.LayerGroup) {
              // recursive
              var subResult = L.GeometryUtil.closestLayer(map, layer.getLayers(), latlng);
              results.push(subResult);
          } else {
              // Single dimension, snap on points, else snap on closest
              if (typeof layer.getLatLng == 'function') {
                  ll = layer.getLatLng();
                  distance = L.GeometryUtil.distance(map, latlng, ll);
              }
              else {
                  ll = L.GeometryUtil.closest(map, layer, latlng);
                  if (ll) distance = ll.distance;  // Can return null if layer has no points.
              }
              results.push({layer: layer, latlng: ll, distance: distance});
          }
      }

      results.sort(function(a, b) {
          return a.distance - b.distance;
      });

      if (results.length > n) {
          return results.slice(0, n);
      } else  {
          return results;
      }
  },

  /**
   * Returns all layers within a radius of the given position, in an ascending order of distance.
     @param {L.Map} map  map to be used for this method
     @param {Array<ILayer>} layers - A list of layers.
     @param {L.LatLng} latlng - The position to search
     @param {?Number} [radius=Infinity] - Search radius in pixels
     @return {object[]} an array of objects including layer within the radius, closest latlng, and distance
   */
  layersWithin: function(map, layers, latlng, radius) {
    radius = typeof radius == 'number' ? radius : Infinity;

    var results = [];
    var ll = null;
    var distance = 0;

    for (var i = 0, n = layers.length; i < n; i++) {
      var layer = layers[i];

      if (typeof layer.getLatLng == 'function') {
          ll = layer.getLatLng();
          distance = L.GeometryUtil.distance(map, latlng, ll);
      }
      else {
          ll = L.GeometryUtil.closest(map, layer, latlng);
          if (ll) distance = ll.distance;  // Can return null if layer has no points.
      }

      if (ll && distance < radius) {
          results.push({layer: layer, latlng: ll, distance: distance});
      }
    }

    var sortedResults = results.sort(function(a, b) {
        return a.distance - b.distance;
    });

    return sortedResults;
  },

  /**
      Returns the closest position from specified {LatLng} among specified layers,
      with a maximum tolerance in pixels, providing snapping behaviour.

      @tutorial closest

      @param {L.Map} map  map to be used for this method
      @param {Array<ILayer>} layers - A list of layers to snap on.
      @param {L.LatLng} latlng - The position to snap
      @param {?Number} [tolerance=Infinity] - Maximum number of pixels.
      @param {?boolean} [withVertices=true] - Snap to layers vertices or segment points (not only vertex)
      @returns {object} with snapped {LatLng} and snapped {Layer} or null if tolerance exceeded.
  */
  closestLayerSnap: function (map, layers, latlng, tolerance, withVertices) {
      tolerance = typeof tolerance == 'number' ? tolerance : Infinity;
      withVertices = typeof withVertices == 'boolean' ? withVertices : true;

      var result = L.GeometryUtil.closestLayer(map, layers, latlng);
      if (!result || result.distance > tolerance)
          return null;

      // If snapped layer is linear, try to snap on vertices (extremities and middle points)
      if (withVertices && typeof result.layer.getLatLngs == 'function') {
          var closest = L.GeometryUtil.closest(map, result.layer, result.latlng, true);
          if (closest.distance < tolerance) {
              result.latlng = closest;
              result.distance = L.GeometryUtil.distance(map, closest, latlng);
          }
      }
      return result;
  },

  /**
      Returns the Point located on a segment at the specified ratio of the segment length.
      @param {L.Point} pA coordinates of point A
      @param {L.Point} pB coordinates of point B
      @param {Number} the length ratio, expressed as a decimal between 0 and 1, inclusive.
      @returns {L.Point} the interpolated point.
  */
  interpolateOnPointSegment: function (pA, pB, ratio) {
      return L.point(
          (pA.x * (1 - ratio)) + (ratio * pB.x),
          (pA.y * (1 - ratio)) + (ratio * pB.y)
      );
  },

  /**
      Returns the coordinate of the point located on a line at the specified ratio of the line length.
      @param {L.Map} map  map to be used for this method
      @param {Array<L.LatLng>|L.PolyLine} latlngs Set of geographical points
      @param {Number} ratio the length ratio, expressed as a decimal between 0 and 1, inclusive
      @returns {Object} an object with latLng ({LatLng}) and predecessor ({Number}), the index of the preceding vertex in the Polyline
      (-1 if the interpolated point is the first vertex)
  */
  interpolateOnLine: function (map, latLngs, ratio) {
      latLngs = (latLngs instanceof L.Polyline) ? latLngs.getLatLngs() : latLngs;
      var n = latLngs.length;
      if (n < 2) {
          return null;
      }

      // ensure the ratio is between 0 and 1;
      ratio = Math.max(Math.min(ratio, 1), 0);

      if (ratio === 0) {
          return {
              latLng: latLngs[0] instanceof L.LatLng ? latLngs[0] : L.latLng(latLngs[0]),
              predecessor: -1
          };
      }
      if (ratio == 1) {
          return {
              latLng: latLngs[latLngs.length -1] instanceof L.LatLng ? latLngs[latLngs.length -1] : L.latLng(latLngs[latLngs.length -1]),
              predecessor: latLngs.length - 2
          };
      }

      // project the LatLngs as Points,
      // and compute total planar length of the line at max precision
      var maxzoom = map.getMaxZoom();
      if (maxzoom === Infinity)
          maxzoom = map.getZoom();
      var pts = [];
      var lineLength = 0;
      for(var i = 0; i < n; i++) {
          pts[i] = map.project(latLngs[i], maxzoom);
          if(i > 0)
            lineLength += pts[i-1].distanceTo(pts[i]);
      }

      var ratioDist = lineLength * ratio;

  // follow the line segments [ab], adding lengths,
      // until we find the segment where the points should lie on
  var cumulativeDistanceToA = 0, cumulativeDistanceToB = 0;
  for (var i = 0; cumulativeDistanceToB < ratioDist; i++) {
    var pointA = pts[i], pointB = pts[i+1];

    cumulativeDistanceToA = cumulativeDistanceToB;
    cumulativeDistanceToB += pointA.distanceTo(pointB);
  }
  
  if (pointA == undefined && pointB == undefined) { // Happens when line has no length
    var pointA = pts[0], pointB = pts[1], i = 1;
  }

  // compute the ratio relative to the segment [ab]
  var segmentRatio = ((cumulativeDistanceToB - cumulativeDistanceToA) !== 0) ? ((ratioDist - cumulativeDistanceToA) / (cumulativeDistanceToB - cumulativeDistanceToA)) : 0;
  var interpolatedPoint = L.GeometryUtil.interpolateOnPointSegment(pointA, pointB, segmentRatio);
  return {
    latLng: map.unproject(interpolatedPoint, maxzoom),
    predecessor: i-1
  };
  },

  /**
      Returns a float between 0 and 1 representing the location of the
      closest point on polyline to the given latlng, as a fraction of total line length.
      (opposite of L.GeometryUtil.interpolateOnLine())
      @param {L.Map} map  map to be used for this method
      @param {L.PolyLine} polyline Polyline on which the latlng will be search
      @param {L.LatLng} latlng The position to search
      @returns {Number} Float between 0 and 1
  */
  locateOnLine: function (map, polyline, latlng) {
      var latlngs = polyline.getLatLngs();
      if (latlng.equals(latlngs[0]))
          return 0.0;
      if (latlng.equals(latlngs[latlngs.length-1]))
          return 1.0;

      var point = L.GeometryUtil.closest(map, polyline, latlng, false),
          lengths = L.GeometryUtil.accumulatedLengths(latlngs),
          total_length = lengths[lengths.length-1],
          portion = 0,
          found = false;
      for (var i=0, n = latlngs.length-1; i < n; i++) {
          var l1 = latlngs[i],
              l2 = latlngs[i+1];
          portion = lengths[i];
          if (L.GeometryUtil.belongsSegment(point, l1, l2, 0.0001)) {
              portion += l1.distanceTo(point);
              found = true;
              break;
          }
      }
      if (!found) {
          throw "Could not interpolate " + latlng.toString() + " within " + polyline.toString();
      }
      return portion / total_length;
  },

  /**
      Returns a clone with reversed coordinates.
      @param {L.PolyLine} polyline polyline to reverse
      @returns {L.PolyLine} polyline reversed
  */
  reverse: function (polyline) {
      return L.polyline(polyline.getLatLngs().slice(0).reverse());
  },

  /**
      Returns a sub-part of the polyline, from start to end.
      If start is superior to end, returns extraction from inverted line.
      @param {L.Map} map  map to be used for this method
      @param {L.PolyLine} polyline Polyline on which will be extracted the sub-part
      @param {Number} start ratio, expressed as a decimal between 0 and 1, inclusive
      @param {Number} end ratio, expressed as a decimal between 0 and 1, inclusive
      @returns {Array<L.LatLng>} new polyline
   */
  extract: function (map, polyline, start, end) {
      if (start > end) {
          return L.GeometryUtil.extract(map, L.GeometryUtil.reverse(polyline), 1.0-start, 1.0-end);
      }

      // Bound start and end to [0-1]
      start = Math.max(Math.min(start, 1), 0);
      end = Math.max(Math.min(end, 1), 0);

      var latlngs = polyline.getLatLngs(),
          startpoint = L.GeometryUtil.interpolateOnLine(map, polyline, start),
          endpoint = L.GeometryUtil.interpolateOnLine(map, polyline, end);
      // Return single point if start == end
      if (start == end) {
          var point = L.GeometryUtil.interpolateOnLine(map, polyline, end);
          return [point.latLng];
      }
      // Array.slice() works indexes at 0
      if (startpoint.predecessor == -1)
          startpoint.predecessor = 0;
      if (endpoint.predecessor == -1)
          endpoint.predecessor = 0;
      var result = latlngs.slice(startpoint.predecessor+1, endpoint.predecessor+1);
      result.unshift(startpoint.latLng);
      result.push(endpoint.latLng);
      return result;
  },

  /**
      Returns true if first polyline ends where other second starts.
      @param {L.PolyLine} polyline First polyline
      @param {L.PolyLine} other Second polyline
      @returns {bool}
  */
  isBefore: function (polyline, other) {
      if (!other) return false;
      var lla = polyline.getLatLngs(),
          llb = other.getLatLngs();
      return (lla[lla.length-1]).equals(llb[0]);
  },

  /**
      Returns true if first polyline starts where second ends.
      @param {L.PolyLine} polyline First polyline
      @param {L.PolyLine} other Second polyline
      @returns {bool}
  */
  isAfter: function (polyline, other) {
      if (!other) return false;
      var lla = polyline.getLatLngs(),
          llb = other.getLatLngs();
      return (lla[0]).equals(llb[llb.length-1]);
  },

  /**
      Returns true if first polyline starts where second ends or start.
      @param {L.PolyLine} polyline First polyline
      @param {L.PolyLine} other Second polyline
      @returns {bool}
  */
  startsAtExtremity: function (polyline, other) {
      if (!other) return false;
      var lla = polyline.getLatLngs(),
          llb = other.getLatLngs(),
          start = lla[0];
      return start.equals(llb[0]) || start.equals(llb[llb.length-1]);
  },

  /**
      Returns horizontal angle in degres between two points.
      @param {L.Point} a Coordinates of point A
      @param {L.Point} b Coordinates of point B
      @returns {Number} horizontal angle
   */
  computeAngle: function(a, b) {
      return (Math.atan2(b.y - a.y, b.x - a.x) * 180 / Math.PI);
  },

  /**
     Returns slope (Ax+B) between two points.
      @param {L.Point} a Coordinates of point A
      @param {L.Point} b Coordinates of point B
      @returns {Object} with ``a`` and ``b`` properties.
   */
  computeSlope: function(a, b) {
      var s = (b.y - a.y) / (b.x - a.x),
          o = a.y - (s * a.x);
      return {'a': s, 'b': o};
  },

  /**
     Returns LatLng of rotated point around specified LatLng center.
      @param {L.LatLng} latlngPoint: point to rotate
      @param {double} angleDeg: angle to rotate in degrees
      @param {L.LatLng} latlngCenter: center of rotation
      @returns {L.LatLng} rotated point
   */
  rotatePoint: function(map, latlngPoint, angleDeg, latlngCenter) {
      var maxzoom = map.getMaxZoom();
      if (maxzoom === Infinity)
          maxzoom = map.getZoom();
      var angleRad = angleDeg*Math.PI/180,
          pPoint = map.project(latlngPoint, maxzoom),
          pCenter = map.project(latlngCenter, maxzoom),
          x2 = Math.cos(angleRad)*(pPoint.x-pCenter.x) - Math.sin(angleRad)*(pPoint.y-pCenter.y) + pCenter.x,
          y2 = Math.sin(angleRad)*(pPoint.x-pCenter.x) + Math.cos(angleRad)*(pPoint.y-pCenter.y) + pCenter.y;
      return map.unproject(new L.Point(x2,y2), maxzoom);
  },

  /**
     Returns the bearing in degrees clockwise from north (0 degrees)
     from the first L.LatLng to the second, at the first LatLng
     @param {L.LatLng} latlng1: origin point of the bearing
     @param {L.LatLng} latlng2: destination point of the bearing
     @returns {float} degrees clockwise from north.
  */
  bearing: function(latlng1, latlng2) {
      var rad = Math.PI / 180,
          lat1 = latlng1.lat * rad,
          lat2 = latlng2.lat * rad,
          lon1 = latlng1.lng * rad,
          lon2 = latlng2.lng * rad,
          y = Math.sin(lon2 - lon1) * Math.cos(lat2),
          x = Math.cos(lat1) * Math.sin(lat2) -
              Math.sin(lat1) * Math.cos(lat2) * Math.cos(lon2 - lon1);

      var bearing = ((Math.atan2(y, x) * 180 / Math.PI) + 360) % 360;
      return bearing >= 180 ? bearing-360 : bearing;
  },

  /**
     Returns the point that is a distance and heading away from
     the given origin point.
     @param {L.LatLng} latlng: origin point
     @param {float} heading: heading in degrees, clockwise from 0 degrees north.
     @param {float} distance: distance in meters
     @returns {L.latLng} the destination point.
     Many thanks to Chris Veness at http://www.movable-type.co.uk/scripts/latlong.html
     for a great reference and examples.
  */
  destination: function(latlng, heading, distance) {
      heading = (heading + 360) % 360;
      var rad = Math.PI / 180,
          radInv = 180 / Math.PI,
          R = 6378137, // approximation of Earth's radius
          lon1 = latlng.lng * rad,
          lat1 = latlng.lat * rad,
          rheading = heading * rad,
          sinLat1 = Math.sin(lat1),
          cosLat1 = Math.cos(lat1),
          cosDistR = Math.cos(distance / R),
          sinDistR = Math.sin(distance / R),
          lat2 = Math.asin(sinLat1 * cosDistR + cosLat1 *
              sinDistR * Math.cos(rheading)),
          lon2 = lon1 + Math.atan2(Math.sin(rheading) * sinDistR *
              cosLat1, cosDistR - sinLat1 * Math.sin(lat2));
      lon2 = lon2 * radInv;
      lon2 = lon2 > 180 ? lon2 - 360 : lon2 < -180 ? lon2 + 360 : lon2;
      return L.latLng([lat2 * radInv, lon2]);
  },

  /**
     Returns the the angle of the given segment and the Equator in degrees,
     clockwise from 0 degrees north.
     @param {L.Map} map:  map to be used for this method
     @param {L.LatLng} latlngA: geographical point A of the segment
     @param {L.LatLng} latlngB: geographical point B of the segment
     @returns {Float} the angle in degrees.
  */
  angle: function(map, latlngA, latlngB) {
    var pointA = map.latLngToContainerPoint(latlngA),
        pointB = map.latLngToContainerPoint(latlngB),
        angleDeg = Math.atan2(pointB.y - pointA.y, pointB.x - pointA.x) * 180 / Math.PI + 90;
    angleDeg += angleDeg < 0 ? 360 : 0;
    return angleDeg;
  },

  /**
     Returns a point snaps on the segment and heading away from the given origin point a distance.
     @param {L.Map} map:  map to be used for this method
     @param {L.LatLng} latlngA: geographical point A of the segment
     @param {L.LatLng} latlngB: geographical point B of the segment
     @param {float} distance: distance in meters
     @returns {L.latLng} the destination point.
  */
  destinationOnSegment: function(map, latlngA, latlngB, distance) {
    var angleDeg = L.GeometryUtil.angle(map, latlngA, latlngB),
        latlng = L.GeometryUtil.destination(latlngA, angleDeg, distance);
    return L.GeometryUtil.closestOnSegment(map, latlng, latlngA, latlngB);
  },
});

return L.GeometryUtil;

}));

/*
  * 版权声明：本文为CSDN博主「Daisen.Z」的原创文章，遵循CC 4.0 BY-SA版权协议，转载请附上原文出处链接及本声明。
  * 原文链接：https://blog.csdn.net/weixin_43464964/article/details/105388859
*/
